1. Field of the Invention
The present invention relates to a frequency unit valve, and more particularly, to a frequency unit valve that is capable of maximally improving a vehicle ride comfort.
2. Description of the Related Art
A shock absorber for a vehicle is mounted on front and rear wheels of the vehicle and absorbs vibration transferred from a road, improving the steering stability and ride comfort. A shock absorber has a piston valve opening/closing structure that forms a passage with a complicated shape to provide various nonlinear damping forces according to an operating speed of a wheel.
In order to improve the ride comfort, the shock absorber for the vehicle allows an oil discharge by mounting a damper in an end portion of a piston rod and mounting a sub-valve in a lower portion of the damper and a free piston moving vertically inside the damper.
Therefore, while the free piston reciprocates within the damper, the operation characteristic of the entire valve system, including the damper, the free piston, and the sub-valve, is changed.
In most valve systems manufactured so far, oil flowing into a damper through a piston rod defines an up stroke and a down stroke of a free piston. However, when a frequency according to the reciprocation of the piston rod is in a high-frequency region, such valve systems may not sufficiently provide an additional damping force. Therefore, problems such as pressure pulsation have not been perfectly solved.